The invention relates to the field of breast implants, and in particular, filler materials for breast implants.
For well over thirty years, women have been undergoing breast augmentation in the United States. Early efforts included free silicone injections. Over the years, free silicone has coalesced into hard nodular breast masses indistinguishable from cancer, and making mammography all but impossible to read. This in turn has led to aggressive surgery such as subcutaneous mastectomy with often less than desirable results.
Later, implants made of liquid silicone contained within a polymer, typically silicone, sac were used. While the silicone of the sac itself was not generally thought to cause a problem, the tendency of the sacs to rupture or leak over long periods of time created disastrous problems for many users.
The presence of free liquid silicone, whether by injection or by rupture of a silicone implant has had serious local and systemic side effects, particularly migration of the free silicone and collection of silicone in major body organs, such as the liver. The presence of free silicone has incited autoimmune responses in many patients causing a severely debilitated state. Even more serious, in some patients the silicone has been found to cause autoimmune responses even when confined to the polymer sac. One study has shown that some women with breast implants produce antibodies against their own collagen, but it is not known whether this might increase their risk of actually developing an autoimmune-like disorder.
A double lumen silicone/saline implant, with an inner silicone filled sac and an outer saline filled sac, was originally thought to be the answer to the problems with the silicone implant, but has proven to have nearly as many faults. For example, the internal silicone sac can rupture leaving the patient in a state of fear and the physician in a state of indecision as how best to handle the situation. If the double lumen implant, now a single lumen implant, is left in place, the problem of autoimmune disorder becomes potentially more likely with transmigration of minute amounts of silicone out of the intact polymer sac.
The problem of side effects caused by silicone can be eliminated by filling the polymer sac with physiological saline solution. While the saline implant has generally eliminated immune system problems, saline filled sacs have been subject to partial deflation. The package insert of the McGhan Biocell.RTM. RTV sac warns that capsular contracture may result in firmness, discomfort or pain in the breast, and/or displacement of the implant. Several published studies have observed a very high incidence of deflation, specifically McGrath et al, "The Safety and Efficacy of Breast Implants for Augmentation Mammaplasty," Plastic & Reconstructive Surgery 74:550 (1984); Williams, "Experience with a Large Series of Silastic Breast Implants," Plastic & Reconstructive Surgery 49:253 (1972); and Grossman, "The Current Status of Augmentation Mammaplasty," Plastic & Reconstructive Surgery 52:1 (1973), the reported incidence of deflation reaching as high as 76%.
The long term cosmetic effects of the saline implant have thus been generally unsatisfactory, the partially deflated sac crinkling, with a wave like effect being felt instead of a full soft breast. The reason for this deflation is speculated as being osmotic pressure, aggravated by a tendency on the part of implanting surgeons to overinflate the sac with saline.
U.S. Pat. No. 4,995,882 has proposed the use of a triglyceride such as peanut oil or sunflower seed oil as a filling for a breast implant, these filling materials having the same average radiographic density as human breast tissue. However, it is known that silicone sac itself interferes with mammography, so utilizing a less interfering filling does not completely solve the mammography problem.
The use of silicone filled implants has now been discontinued in the United States in all cases except for breast reconstruction necessitated by mastectomy for cancer treatment. In view of the safety problems presented by silicone, the search for a safe replacement material has become important.